1. Field of the Invention
The present invention relates to a film formation mask for highly precise pattering, in which slit-like openings are provided in a metal foil, and more particularly, to a film formation mask for use in a vapor deposition process of an organic material in manufacturing an organic electroluminescence display device.
2. Description of the Related Art
In manufacturing an organic electroluminescence (EL) display device, as a process of forming an organic compound layer, there is known a method of forming a pattern of an organic material by using a film formation mask in which openings are provided in a metal foil. In this method, a thin film is formed by causing a vapor deposition material which has passed through the openings in the film formation mask to reach a substrate. This method is widely used, because a pattern of an organic film may be formed without using lithography. In recent years, a more and more finer pixel pattern is required. Thus, as the film formation mask, a tension mask is widely used, in which a thin metal foil having a highly precise opening pattern formed therein is attached to a frame. In particular, a slit-like opening pattern is widely used from the viewpoint of the ratio of area of openings in the mask and openings in a pixel.
For example, Japanese Patent No. 4,173,722 discloses a film formation mask having an ordinary slit-like opening pattern formed therein. In this film formation mask, the lengths, the shapes, and the pitches of the slit-like openings are uniform and the ends of the openings are aligned, and thus, the shapes and the positions of the metal foil between the openings are the same. Japanese Patent Application Laid-Open No. 2007-234678 discloses a film formation mask in which the ends of slit-like openings are gradually tapered toward the tips. Also in this case, the lengths, the shapes, and the pitches of the slit-like openings are uniform and the ends of the openings are aligned, and thus, the shapes and the positions of the metal foil between the openings are the same. Further, Japanese Patent Application Laid-Open No. 2003-332059 discloses a mask having bridges formed between openings. The ends of odd-numbered columns of openings and the ends of even-numbered columns of openings are staggered, and thus, the mask is less liable to be deformed by tension applied to the film formation mask and is highly precise, which improves the precision of the vapor deposition film.
A film formation mask having a fine opening pattern in which multiple slit-like openings are arranged has a problem that the sides of metal foil portions provided on both sides of the slit-like opening in a short side direction thereof are brought into contact with each other by vibrations. Such vibrations are caused when the film formation mask is brought into contact with a glass substrate or when the film formation mask is peeled off in a film formation process, or, when the mask is transferred. When such contact is caused, the slit-like openings are partly closed, and as a result, a problem arises that a film formation pattern in a desired shape cannot be formed. In particular, when the amount of an organic material deposited on the film formation mask increases, the state in which the sides of the metal foil portions are in contact with each other is maintained by the organic material deposited on the mask, and hence the area of closed portions of the slit-like openings increases.
Further, in the film formation mask disclosed in Japanese Patent Application Laid-Open No. 2003-332059, vibrations of the metal foil portions are scarcely caused by external vibrations because the bridges are formed, and thus, the above-mentioned problem that the slit-like openings are closed does not arise. However, the ratio of the area of the openings becomes smaller, and thus, the aperture ratio of a pixel becomes smaller with respect to the mask. When light is emitted with the same luminance, an increase in power consumption or a decrease in life is caused.